The invention pertains generally to polymer modification by additives and particularly to the lowering of surface energy of vinyl polymers by the inclusion therein of a small amount of a low surface-energy oligomer.
While Teflon is an excellent material with an extremely low surface-energy, it is not without disadvantages. Teflon cannot be extruded and it is expensive. Storage of Teflon sheets is complicated by Teflon's tendency to bow. Many vinyl compounds are also excellent materials and they do not have the above disadvantages of Teflon. Unfortunately, the surface energy of these compounds are much higher than Teflon. Thus, if the surface energy of these vinyl compounds could be lowered, their wettability would decrease and thus they would have many additional uses as, e.g., films, abhesives, filaments, and structural materials.
Since the surface energy of a polymer is dependent upon the chemical constitution of the surface layer of the polymer, one technique for decreasing the wettability of a polymer is modifying the chemical composition of the surface. Desirably, the alteration is accomplished without proportionately altering the bulk properties of the polymer.
The most successful modification of the surface composition of solid vinyl polymers has been obtained by the adsorption of partially fluorinated esters at the polymer-air interface during the formation of this interface. These additives were compounds of comparatively small molecules, and some were crystalline. Additives of those types provided limited benefit due to poor resistance to abrasion of the surface and to poor ability to migrate to the surface of the polymer after the surface has been worn, i.e., to poor self-healing ability.